I think Jon is talking about the time it takes for the REPL to evaluate the first expression you enter, not the speed of Scala per se.
Regarding video vs. being in the room: I have to say I prefer watching a lecture as a video. It allows me to adjust the pace. So when the prof said something that I need to digest (or when he says something that prompts a line of thought that I want to think through to the end), I can just pause the video and think about it carefully. I'd miss half the lecture if I did that in a live lecture.
Similarly if the Prof is still explaining something I already understood, I can simply fast forward. And if I missed something the prof said because I was distracted, I can rewind.
This post has been edited by sepp2k: 27 September 2012 - 12:47 AM